1. Technical Field of the Invention
The present invention relates generally to an angular rate sensor which may be employed in an attitude control system for automotive vehicles, a hand-shake compensating system for video cameras, or a gyroscope of a navigation system for moving objects and a method of improving output characteristics of an angular rate sensor.
2. Background of Related Art
Japanese Patent First Publication Nos. 8-210860, 8-152328, and 6-241815 teach conventional angular rate sensors which include an oscillator mounted on a base through a supporter. The oscillator is vibrated by the Coriolis force produced by the angular rate acting thereon during excitation, which is monitored to determine the angular rate.
Such angular rate sensors, as will be discussed later in detail, encounter several problems leading to errors of sensor outputs which will result in lack of reliability and confidence of sensor operations.
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide an angular rate sensor designed to measure an angular rate acting on a moving object with high accuracy.
It is a further object of the invention to provide a method of adjusting a physical structure of an angular rate sensor to improve an output characteristic thereof.
According to one aspect of the present invention, there is provided a method of adjusting an oscillation characteristic of an oscillator of an angular rate sensor, the oscillator having a given length and being shaped to have a plurality of longitudinal edges, the oscillator being excited by input of an excitation signal to oscillate in a first direction perpendicular to the length of the oscillator and, when the angular rate sensor undergoes an angular rate during excitation of the oscillator, oscillating in a second direction perpendicular to the length of the oscillator to provide an output indicative of the angular rate, which comprises the steps of: (a) applying to the oscillator an ac voltage having a resonant frequency, at which the oscillator resonates in the first direction, to oscillate the oscillator, (b) monitoring an output signal of the oscillator during oscillation of the oscillator by application of the ac voltage; and (c) adjusting the oscillation characteristic of the oscillator so as to decrease an amplitude of the monitored output signal of the oscillator to minimize undesired oscillations of the oscillator in the second direction when excited by the input of the excitation signal.
In the preferred mode of the invention, the adjusting step removes a portion of the oscillator to adjust the oscillation characteristic of the oscillator. The removed portion of the oscillator may be one of the longitudinal edges of the oscillator.
The oscillator is a fork oscillator including a pair of arms and a connecting portion connecting ends of the arms. The adjusting step removes a portion of at least one of longitudinal edges of the arms to adjust the oscillation characteristic of the oscillator.
The adjusting step may remove at least one of an longitudinal edge portion of one of the arms leading to the connecting portion, an edge portion of the connecting portion extending in a lengthwise direction of the arms, and a portion of the longitudinal edges of the oscillator extending over a connection between one of the arms and the connecting portion.
The oscillator may alternatively include a single oscillating portion made of a polygonal rod member whose end is fixed on the angular rate sensor. The adjusting step may remove a portion of the oscillating portion leading to the fixed end or alternatively remove a central portion of a longitudinal edge of the oscillating portion to adjust the oscillation characteristic of the oscillator.
The adjusting step may machine a portion of the oscillator in a lengthwise direction or alternatively in a depthwise direction to adjust the oscillation characteristic of the oscillator.
The oscillator is made of a piezoelectric element.
According to the second aspect of the invention, there is provided a method of adjusting an output characteristic of an angular rate sensor which includes a first oscillator having a given length, shaped to have a plurality of longitudinal edges, excitation means responsive to input of an excitation signal for exciting the first oscillator to oscillate in an excitation-axis direction perpendicular to a longitudinal center line of the first oscillator, and a second oscillator having a given length, shaped to have a plurality of longitudinal edges having pickup means for picking up oscillations of the second oscillator in a pickup-axis direction perpendicular to a longitudinal center line of the second oscillator, which comprises the steps of: (a) applying an ac voltage having a resonant frequency, at which the first oscillator resonates in the excitation-axis direction, to the excitation means to oscillate the oscillating portion of the first oscillator; (b) monitoring an output of the pickup means during oscillation of the first oscillator by application of the ac voltage; and (c) adjusting oscillation characteristics of the first and second oscillators so as to decrease an amplitude of the monitored output of the pickup means to minimize undesired oscillations of the second oscillator in the pickup-axis direction produced during oscillation of the first oscillator by the excitation means.
In the preferred mode of the invention, the adjusting step removes portions of the first and second oscillators to adjust the oscillation characteristics of the first and second oscillators. Each of the removed portions of the first and second oscillators may be one of the longitudinal edges of corresponding one of the first and second oscillators.
Each of the first and second oscillator may be a fork oscillator including a pair of arms and a connecting portion connecting ends of the arms. In this case, the adjusting step removes a portion of at least one of longitudinal edges of the arms of each of the first and second oscillators to adjust the oscillation characteristic of the oscillator.
The adjusting step may remove at least one of an longitudinal edge portion of one of the arms leading to the connecting portion of each of the first and second oscillators, an edge portion of the connecting portion extending in a lengthwise direction of the arms of each of the first and second oscillators, and a portion of the longitudinal edges extending over a connection between one of the arms and the connecting portion of each of the first and second oscillators.
According to the third aspect of the invention, there is provided an angular rate sensor for determining an angular rate of rotation when the angular rate sensor experiences the rotation about a given axis, which comprises: (a) an oscillator made of a piezoelectric element including at least one pair of arms and a connecting portion connecting ends of the arms; b) a drive electrode formed on an outer wall of the oscillator, the drive electrode being responsive to input of an excitation signal to oscillate the arms of the oscillator in a first direction perpendicular to length of the oscillator; (c) a pickup electrode formed on the outer wall of the oscillator, the pickup electrode electrically picking up oscillations of the arms in a second direction different form the first direction which indicate the angular rate acting on the angular rate sensor; and (d) an uneven portion formed on a portion of the oscillator near a connection of the connecting portion and the arms for adjusting an oscillation characteristic of the oscillator.
In the preferred mode of the invention, the uneven portion occupies a length of at least one of the arms which extends from the connection and which corresponds to 170% or less of a dimension of the connecting portion in a lengthwise direction of the one of the arms, a portion of the connecting portion ranging from the connection to 70% or less of a dimension of the connecting portion in the lengthwise direction of the arms, or alternatively the both.
According to the fourth aspect of the invention, there is provided a method of adjusting an oscillation characteristic of an oscillator of an angular rate sensor, the oscillator being made of a piezoelectric element shaped to have a plurality of longitudinal edges, including at least one pair of arms and a connecting portion connecting ends of the arms, the oscillator having disposed thereon an excitation electrode and a pickup electrode, the arms being excited by input of an excitation signal through the excitation electrode to oscillate in a first direction perpendicular to length of the arms and, when the angular rate sensor undergoes an angular rate during excitation of the arms, oscillating in a second direction different from the first direction to provide an output signal indicative of the angular rate through the pickup electrode, comprising the steps of: (a) applying an ac voltage to the excitation electrode to oscillate the arms in the first direction; (b) monitoring an output signal of the oscillator through the pickup electrode during oscillation of the arms by application of the ac voltage; and (c) forming an uneven portion on a portion of the oscillator near a connection of the connecting portion and the arms so as to decrease an amplitude of the monitored output signal of the oscillator to minimize undesired oscillations of the oscillator in the second direction when excited by the input of the excitation signal.
In the preferred mode of the invention, the uneven portion occupies a length of at least one of the arms which extends from the connection and which corresponds to 170% or less of a dimension of the connecting portion in a lengthwise direction of the one of the arms, a portion of the connecting portion ranging from the connection to 70% or less of a dimension of the connecting portion in the lengthwise direction of the arms, or alternatively the both.
The uneven portion forming step removes material from the oscillator to form the uneven portion.
The uneven portion forming step may machine the oscillator in the lengthwise direction of the arms to form the uneven portion or alternatively in a depthwise direction of the oscillator to form the uneven portion.
According to the fifth aspect of the invention, there is provided an angular rate sensor for determining an angular rate of rotation when the angular rate sensor experiences the rotation about a given axis, which comprises: (a) an oscillator made of a piezoelectric element including at least one pair of arms and a connecting portion connecting ends of the arms, the arms being excited by input of an excitation signal to oscillate at a first frequency in a first direction perpendicular to length of the arms and, when the angular rate sensor undergoes an angular rate during excitation of the arms, oscillating at a second frequency in a second direction different from the first direction to provide a signal indicative of the angular rate; and (b) a supporting member mounted on a base to hold a node portion of the oscillator, the supporting member having a narrower portion which is so shaped that a frequency difference between the first and second frequencies lies within a preselected range.
In the preferred mode of the invention, the narrower portion of the supporting member is made of a sintered metal.
The supporting member is of an H-shape and also includes first and second members which extend substantially in parallel and which are connected through the narrower portion. The first member is attached to the connecting portion of the oscillator. The second member is attached to the base.
The narrower portion has a length oriented substantially in alignment with a longitudinal center line of the oscillator extending between the arms.
According to the sixth aspect of the invention, there is provided a manufacturing method of an angular rate sensor comprising the steps of: (a) a preparing an oscillator made of a piezoelectric element, including at least one pair of arms and a connecting portion connecting ends of the arms, the arms being excited by input of an excitation signal to oscillate at a first frequency in a first direction perpendicular to length of the arms and, when the angular rate sensor undergoes an angular rate during excitation of the arms, oscillating at a second frequency in a second direction different from the first direction to provide an output signal indicative of the angular rate: (b) installing the oscillator on a base through a supporting member, the supporting member having a narrower portion; (c) applying an ac voltage to the oscillator to oscillate the arms in the first direction; (d) monitoring an output signal from the oscillator during oscillation of the arms by application of the ac voltage to determine a frequency difference between the first and second frequencies; and (e) changing torsional rigidity of the narrower portion of the supporting member so that the frequency difference determined in the monitoring step lies within a preselected range.
In the preferred mode of the invention, the torsional rigidity changing step modifies shape of the narrower portion of the supporting member to change the torsional rigidity. For example, the torsional rigidity changing step removes material from the narrower portion or attaches a given member to the narrower portion to change the torsional rigidity.
According to the seventh aspect of the invention, there is provided a method of adjusting an oscillation characteristic of an oscillator of an angular rate sensor, the oscillator being made of a piezoelectric element, including at least one pair of arms and a connecting portion connecting ends of the arms, the arms being excited by input of an excitation signal to oscillate at a first frequency in a first direction perpendicular to length of the arms and, when the angular rate sensor undergoes an angular rate during excitation of the oscillator, oscillating at a second frequency in a second direction different from the first direction to produce an output signal indicative of the angular rate, which comprises the steps of: (a) applying an ac voltage to the oscillator to oscillate the arms in the first direction; (b) monitoring an output signal from the oscillator during oscillation of the arms by application of the ac voltage to determine a frequency difference between the first and second frequencies; and (c) changing torsional rigidity of the narrower portion of the supporting member so that the frequency difference determined in the monitoring step lies within a preselected range.
In the preferred mode of the invention, the torsional rigidity changing step modifies shape of the narrower portion of the supporting member to change the torsional rigidity.